In the production of today's integrated circuits, optical lithography is one of the key manufacturing techniques. In order to cope with the ongoing miniaturisation of integrated circuits or other devices and its associated problems, low k1 solutions, i.e. solutions allowing high resolving power lithography, are often applied.
Control of critical dimension (CD) and of the resist profile is increasingly important in low-k1 lithography in order to guarantee the imaging quality for these solutions. This control is even more difficult in thin resist lithographic processing due to chemical interactions occurring at the resist surfaces. The critical dimension and resist profile control typically are affected significantly by chemical interactions with the top surface of the device and possibly with underlying layers of the device such as an anti-reflective coating. These chemical interactions may result in contamination, e.g. airborne contamination.
Implementation of immersion lithography further lays a burden on critical dimension and resist profile control since more sources of chemical interaction can play a role. For example, leaching of photo-active material from the resist into the immersion liquid, or diffusion of the immersion liquid into the resist may occur. One solution to prevent possible contamination by the immersion liquid is the use of a top coat. Nevertheless, whether a top coat is used or not, it is expected that critical dimension control and profile control in immersion lithography will be susceptible to more variations compared to dry lithography.